Pipelines are typically used to carry liquids and gas, such as natural gas, oil, and so on, throughout all points in a distribution network that is used to bring these products from their source, such as a natural gas field or oil field, or a refinery, to their place of consumption such as a home or industry. In this distribution network, the pipelines may need to be located in the wilderness, either underground or above ground, most likely over very great distances. Further, these pipes must also form the network in any sort of refinery or other related operation, and also form the network that supplies end users, such as homes and industries, with the contained product. Any network of such piping that is to be found above ground or underground in the outdoors, may be exposed to and need to endure heat, cold, ground movement, lightning, ground electrical potential, water, chemicals, and physical abuse from maintenance, among other things. Any piping network that is in an urban area or is within an industrial setting such as refinery, or similar, must endure most of these problems and also any other rigours that maybe placed on the pipeline, such as being exposed to other utilities such as hydro, and also be extremely safe so as to be acceptable for being used within an inhabited area.
A ground electrical potential may occur in a buried pipe due to induction from nearby hydro wires or high voltage DC wires (such as used in some transit systems). Further, a portion of the pipe may be electrified by being placed in a cathodic protection mode in order to preclude corrosion of the pipe. Such cathodic protection involves purposely introducing a negative electrical potential to the section of the pipe that is to be protected. It is undesirable that the potential be introduced to a longer section of the pipe than necessary.
These pipes must also carry various types of products, at possibly low or very high pressures, or even under changing pressure conditions. They must also be able to carry these products in different volumes and therefore the pipelines must be of various sizes.
In general, these pipelines are installed in sections that are quite lengthy. Smaller sections of perhaps ten feet to fifty feet are welded one to another in order to form a fairly lengthy section that essentially becomes a monolith that is perhaps several hundred yards to hundreds or thousands of miles long. These pipelines are generally made of a steel alloy, and since they are welded together the monolith that is formed is essentially a rigid structure with virtually no physical flexibility to it. Also, since steel is the main component of the pipeline, they are good conductors of electricity. Resultingly, such pipelines inherently have two problems. Firstly, any structure that is buried within the ground or is sitting the ground is susceptible to any movement within the ground. Such ground movement may cause bending moments or torsion within the pipeline. Over a large distance, the pipeline could very easily be exposed to movements large enough to break the pipeline or at least stress the pipe line enough that the highly pressurized gas within it would cause the pipeline to fracture. Secondly, an electrical potential can develop in the pipeline for a number of reasons including lightning, ground electrical potential, stray hydro lines, and so on, thereby electrifying the pipeline. In order to overcome these problems, electrically insulating joints are installed every so often in a pipeline. These joints provide electrical insulation between sections of the pipeline. Further, these joints are designed and constructed to have a higher strength than the pipeline such that in a bending mode the joint will survive when the pipeline breaks.
Moisture presents a problem in terms of conduction of electricity, static or otherwise, to and around pipelines. Electrically insulating joints that are installed in pipelines must not be affected by moisture in that they must remain insulating even when exposed to moisture. Further, such joints must not corrode or generally break down due to moisture.
It is necessary that any pipeline be sectioned off, with the resulting sections being electrically insulated one from the other in order that any electrical potential that may be present in any part of the pipeline not be transmitted very far along the pipeline. This would preclude any electrical potential from migrating very far along the pipeline and thereby creating an electrically unsafe conditions. Such an electrically unsafe condition may potentially cause an explosion or may cause a potentially dangerous condition for someone who may be working on the pipeline, in an industry served by the pipeline, in a refinery, at the source of the product, or in a home.
In its most basic form, a joint comprises two fairly short pieces of pipe, one at each end of the joint and a seal between the two pieces of pipe. In order to properly receive the seal, the two ends of the pipes facing one another each terminate in a flange, the two flanges co-operate with one another and with the seal therebetween in order to form a "leak-proof" joint. Such a joint is welded at each of its two open ends to a pipe, thus joining the two pipes in sealed relation.
Such joints are typically installed into a pipeline as the pipeline itself is constructed. It is also possible, however, to install joints into an already existing pipeline, which may be necessary for a variety of reasons such as, if there is a break in the pipeline, if there is a need for further electrical insulation, and so on. The easiest way to fix a break in the pipeline is to cut the pipeline at the break and to install a joint at that point. Further, it may also be necessary to put additional joints in a section of pipeline if it is found that additional electrical insulators are required.
Some types of joints, whether they are being installed when the pipeline is being installed, or joints are being installed into an already existing pipeline, can be assembled "in the field" as they are installed onto the pipeline. This is not an ideal situation, however, since the weather conditions may make proper assembly and installation of the joint difficult. There is little or no control over quality of the work that is done in terms of assembly of the joint, and there is most likely no way of testing the joint before it must actually function in the pipeline. Further, the joint is most likely going to be built using less that an ideal method, in that it is virtually impossible to use a fully automated method, or at least a precise production line method, as could be used in a factory. Therefore, it is preferable that a joint be constructed in a factory since any preferred type of method of assembly could be employed, and the quality of the joint could be closely monitored and also be subsequently tested. Further, the installation of the joint to the pipeline in the field would be much quicker if the joint merely had to be welded, or otherwise connected, to the two pieces of pipe that it is being connected to.
In any given pipeline, there is always the chance of the pipeline breaking due to the ground shifting, corrosion of the pipe, careless maintenance, fatigue, and so on. Ideally, the pipeline would not break, neither the pipe itself nor at a joint, but this is unfortunately very unrealistic.
Pipelines must conform to very rigorous standards and are made to a certain physical standard that is generally deemed very safe, depending on the size of the pipeline, the use of the pipeline, and so on. Any joint that is to used within the pipeline, therefore must be capable of withstanding the same pressures and forces, including bending moments, as the pipeline itself, otherwise the joints will be the weak link in the chain and will break. Unfortunately, manufacturers often do not build joint stronger than the pipe that the joint is connected to, and the joint ends up breaking.
Further, a factor that must be considered over and above the actual physical strength of the material that is used to form the joint, is the actual strength of the material used to seal the joint. A joint must be sealed in order to preclude pressurized gas within from escaping from the interior thereof. Virtually all joints have included therein a physical seal that is typically made of a plastic compound which forms a seal between the two abutting pieces of metal in the joint such that any pressurized gas contained within the pipe cannot escape through the seal. Typically, some sort of plastic seal is used because the plastic can provide a highly leak resistant seal between two interfacing metal pieces, and also the plastic can help provide a physically strong joint that is also slightly flexible, as required. In conjunction with the plastic material, an O-ring, probably of a synthetic rubber compound, is used to provide an extremely tight and highly reliable seal. The O-rings should be considered as the primary seal between the pieces of pipe and the plastic separating the pipe. Any other plastic components that are used to separate the pipes or are used in conjunction with covering and protecting any parts of the joint are considered to be secondary seals.
This sort of joint can be found in the prior art and is quite well known. It has been shown, through empirical evidence, that many of these types of joints that seem to satisfy the criteria of being a properly sealed joint, fail far more often than is acceptable.
Further, the joints must also provide adequate electrical insulation between two adjacent pipe length, even when the pipeline is installed in wet ground or is above ground and is exposed to moisture. Further, any connectors that are used to form or fasten the joint, or any materials that are used to weather proof the joint must also be physically protected so as to not experience physical degradation due to environmental exposure or endure damage unnecessarily while being installed, repaired, or for whatever reason.
Any type of joint that is used must be manufactured in more than one size since a variety of sizes of pipeline must be accommodated. Accommodating every size of pipeline can be accomplished by having a size of joint that is suitable for each size of pipeline, or by having joints that can be adapted, probably through some sort of physical adaptor, to fit more than one size of pipeline.